Inoculants for cast iron



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States 2,955,933 Patented Oct. 11, 1960 INOCULANTS FOR CAST IRON Robert W. Freeman, St. Catharines, Ontario, Canada, assignor to Union Carbide Corporation, a corporation of New York No Drawing. Filed Nov. 17, 1958, Ser. No. 774,108

15 Claims. (Cl. 75-123) This invention relates to the manufacture of cast iron and, more particularly, to a new process for treating cast iron and a new addition alloy for use in this process.

Cast iron is a high-carbon ferrous metal having varying chemical constituents and varying physical properties. White cast iron contains combined carbon in the form of iron carbide and is hard, brittle, and difficult to machine. By the use of certain addition agents some of the iron carbide can be rendered unstable and made to dissociate to iron and free carbon, the free carbon being in the form of graphite inclusions. An ironcarbon alloy having such graphite inclusions embedded in a matrix of pearlitic or ferritic steel is known as a gray cast iron. Because of the low cost of production and high mechanical properties of gray cast iron, much research has been conducted to improve the methods of making gray cast iron and to provide improved addition agents, or inoculants as they are called. A particular goal of this research has been to produce a gray cast iron having a preferred type of graphite size and distribution pattern as well as a preferred matrix of pearlite, rather than the softer ferrite.

Numerous inoculants have been proposed to produce what. is known in the industry as type A graphite distribution. This designation of the American Foundrymens Society system for classifying cast iron refers to a cast iron wherein graphite flakes are uniformly dispersed in the matrix with the flakes oriented in random directions. The presence of graphite in this form results in a cast iron that is highly machinable, resistant to wear and has high vibration. damping characteristics; whereas if the graphite arrangement exhibits interdendritic segregation, superimposed flake sizes or rosette groupings, there will be a reduction in the physical properties and machineability characteristics of the cast iron.

In addition to establishing a type A graphite distribution, commercial inoculants also attempt to reduce the depth of chill in the iron. Chilling occurs at the surface and especially at corners or at other light sections where freezing occurs rapidly. Rapid cooling causes formation of hard iron carbide thus making these corners and light sections brittle and difiicult to machine.

It has been the experience of foundrymen that commerical inoculants used to overcome the above described defects produce other undesirable features in the cast iron. For example, those commercial inoculants which accomplish their intended purpose to produce a type A graphitic structure and to reduce depth of chill fall short of complete usefulness in that they simultaneously promote the formation of secondary ferrite in a matrixan addition alloy which will sharply reduce the chill depth in the manufacture of cast iron products.

It is a further object of the present invention to provide an addition alloy which will produce a fully pearlitic matrix in cast iron.

Other aims and advantages of the invention will be apparent from the following description and appended claims.

According to the present invention these objects are accomplished by providing an alloy comprising as its essential ingredients silicon, at least one of the metals from the group consisting of tin and antimony, and minor amounts of manganese and zirconium, and the balance substantially all iron, which can be added as a ladle addition to molten iron.

The silicon content should be between 48 and 62 percent by weight, and is preferably between 51 and 55 percent. The tin content should be between 5 and 20 percent by weight, and preferably between 14 and 16 percent. Manganese and zirconium should be present in an amount between 4 and 6.5 percent by weight of each and preferably between 4.5 and 6.0 percent of each.

It has been found that antimony may be used to replace tin but that different amounts are required. In an alloy of this invention, wherein antimony replaces tin, the antimony content should be between 10 and 40 percent by weight, and preferably between 29 and 31 percent; the silicon content should be between 36 and 58 percent by weight, and preferably between 42 and 45.5 percent; manganese and zirconium should be present in amounts between 3 and 6 percent by weight of each, and preferably between 3.5 and 5 percent of each; and the balance substantially all iron.

When antimony is used to replace only a part of the tin, approximately twice as much antimony is required to replace a given amount of tin. For example, if antimony is to replace one half the tin in the preferred alloy composition, which usually contain 15 percent tin, the alloy should consist of about 15 percent by weight antimony and 7.5 percent by weight of tin. The silicon content should be between 43 and 53 percent by weight and the amounts of manganese and zirconium should be between 4.0 and 4.50 percent by Weight of each. For varying mixtures of the addition metals tin and antimony, the amount of silicon, manganese and zirconium should be proportional to the ranges given in the preceding paragraphs.

To show the amounts of tin and antimony that can be used in combination, two equations defining the upper and lower limits were derived. These positive solutions of these equations give the ranges of tin and antimony to be used when (l) a maximum amount of the addition metals tin and antimony is desired to be added and (2) when a minimum amount of the additions metals is to be added.

Percentage of 40peroentage of antimony Percentage of 1t)pt=ercentage of antimony By substituting in the equations the' amount of tin.

used, for example, the solution of Equation 1 will yield the maximum amount of antimony that may be added to maximum and'minimum amounts of antimony to be Therefore, it is seen that if 4rpercent tin is used in the alloy, the amount of antimony needed is from 2 to 32 percent. If 5 percent tin is used Equation 2 will yield an amount of antimony neededequal to zero which is in agreement with the earlier stated ranges of tin required for when tin is used alone, 5 percent tin will-satisfy the requirements of the alloy of this invention. 1

The exact amount of the constituents of the alloy will vary within the ranges given, depending on the type of cast iron treated. The amount of silicon added to the molten iron should be such as to field a final cast iron product having a silicon content up to about 2.3 percent by weight. Furthermore, the alloy of this invention requires that the weight ratio of silicon to tin or antimony, depending on which is used, in the final cast iron product be about 46 to l for tin and about 23 to l for antimony. Therefore, it is seen that alloys may be prepared for use as ladle inoculants in cast iron production wherein the ranges of silicon and tin, or silicon and antimony, are such as to produce cast iron containing about 2.3 percent by weight of silicon and a silicon-to-tin ratio of about 46 to 1, or a silicon-to-antimony ratio of about 23, to 1.

When the inoculant alloy is to be-c'omposed of an aggregate of tin and antimony rather than being composed of only one of these addition metals, the siliconto-tin-plus-antimony weight ratio must similarly be maintained at certain values. The required ratio of silicon-totin-plus-antimony may be computed by proportions using the ratios required for the individual use of tin or antimony as references; or the following convenient formula may he used:

cast-product over the silicon content of the molten iron bath beforeaddition of the inoculant and computed as a percent by weight of the molten iron bath. X is the percent by weight of tin in the inoculant and Y is the percent by weight of .antimony in the inoculant By giving values to either of two unknowns, thethird value can easily be solved. Applying the formula to specific examples, assume that it is intended to raise the silicon content from 2.0 to 2.3 percent, or an addition .of 0.30 percent, by means ofthe inoculant of this invention. To solve this equation for the required amount of antimony when various levels of tin are known, say 5 percent, merely substitute in the equation thusly:

0.30(2X5+Y)=6. V Y: or add 10 percent antimony at 0% tin 20% oradd .20. percent antimony contentincreases. In thezevent that certain tin-antimony alloys are available and it is required to know how much silicon should be added, merely, substitute the known values of tin and antimony for X and Y respectively, and solve for Z, the amount of silicon needed. For example, if 5 percent tin and 10 percent antimony are used Z(10+ 10) =6 Z=f0.30 percent silicon In certain instances, as when large. castingsare poured, a final silicon content in thecastproduct of only about 1.5 percent by weight may be. sought. .In those cases where the final silicon content is between 1.5 and 2.3 percent by weight, the silicon-to-tin Weight ratio in the final best product should be between 35 to land 46 .to 1; and the silicon-to-antimony weight ratio in the final cast product should be between 17 to'l and 23 to l; and for mixtures of tin and antimony, the ratios should be proportional to these figures.

In summary, the inoculant alloy is to be composed .of tin and/or antimony, plus silicon, manganese and zirconium; the amount of each of the last three elements present being dependent on whether tin is used alone, or antimony is used alone, or tin and antimony are used together. Furthermore, the ratio of silicon to tin and/or antimony must be regulated according to the ranges hereinbefore set forth. Equations 1 and 2 should be used to determine the maximum and minimum amounts of tin and antimony required when these two metals are used together in the aggregate. The amounts of manganese and zirconium. being proportional to the amount of each addition metal, tin or antimony, used in the aggregate. Equation 3 conveniently defines the relationship of silicon to tin and antimony when the two are used in the aggregate or the ratios of silicon-to-tin-plus-antimony may be computed by proportions.

In addition to the primary constituents listed above, the alloy may contain other elements in minor quantities to aid in the control, of proper graphite distribution'and chill reduction. These elements include beryllium, magnesium, calcium, strontium, barium, cerium and aluminum. Accordingly, the present alloy may contain up to 5 percent by weight of any of the above elements, or combinations of two or more elementstogive additional benefits. I

The effectiveness of the alloys of the present invention as inoculants for gray cast iron has been experimentally substantiated. An alloy was prepared containing by weight approximately 15 percent tin, 50 percent silicon, 5.5 percent manganese, 5.5 percent zirconium, and the balance substantially all iron. The alloy was crushed to inch by inch size and was used as aladle inoculant in a 120 pound induction-melted heat of cast iron. The cast product had a chemical analysis of silicon and tin of 2.23 percent and 0.044 percent, respectively. Metallographic examination of the cast iron product, which had a total carbon content of 3.4 percent, showed that the microstructure was entirely pearlitic and that a typeAv graphite distribution was achieved. Furthermore, little or no chill occurred in the cast section. g

In another experiment, antimony was substituted for tin and an alloy was prepared consisting by weight of about 18percent antimony, 5-2 percent silicon, 5 percent manganese, Spercent zirconium, and the balance substantially all iron. This alloy, when added tothe ladle of molten iron, produced a gray castiron containing approximately 2.5 percent silicon and 0.1 percent antimonyr This cast iron also exhibited a completely pearlitic matrix microstructure .free of ferrite and had a type A graphite-distribution. In addition, little or no chill was observed inthecastsection.- H v a I It was also discovered that the alloys of the present invention have desirable effects on the heat resistance characteristics of cast iron. When castingsof gray iron are subjected to elevated temperatures, an increase in volume takes place. This increase in size, or growth as it is called, is serious when the size of a cast product is critical. Such growth is generally attributed to the breakdown of iron carbide in the pearlite matrix at elevated temperatures to ferrite and graphite, these constituents of iron carbide occupying a larger volume than the iron carbide itself. The alloy of the present invention, when used as a cast iron inoculant, stabilizes the pearlitic structure to such .an extent that growth of castings is materially lessened at elevated temperatures as well as at room temperatures.

Tests were conducted to demonstrate the outstanding growth preventing characteristics of this alloy wherein a prior commercial alloy was used to inoculate one sample of a cast iron heat designated Sample A and an alloy of the present invention was used to inoculate another portion of the same heat designated as Sample B. The prior commercial inoculant had the following composition by weight: 62.5 percent silicon, 6 percent manganese, 6 percent zirconium, and the balance iron. The alloy of the present invention consisted by weight of 12.75 percent tin, 49.5 percent silicon, 5.75 percent manganese, 5.5% zirconium, and the balance substantially all iron. Each cast specimen was heat-treated at 690 C. for one hour, furnace-cooled to 350 C. and finally air-cooled to room temperature. This heat treatment was performed 3 times on both samples. The specimens were accurately measured before heating and remeasured after each cooling. The following results of the three-cycle heat-treatment were obtained showing the improvement in results with In summary, alloys produced in accordance With the ranges and relationships disclosed herein give an outstanding number of beneficial results in cast iron, namely, type A graphite distribution, fully pearlitic matrix microstructure, great chill depth reduction and improved heat resistance, which heretofore had not been known in one inoculant.

What is claimed is:

1. A method of treating molten iron for producing iron castings having a type A graphite distribution in a fully pearlitic matrix which comprises adding to a bath of molten iron an alloy consisting essentially of a metal selected from the group consisting of tin and antimony, the amount of tin in the alloy being between 5 and 20 percent by Weight when the metal selected is tin, and the amount of antimony in the alloy being between and 40 percent by weight when the metal selected is antimony, silicon in an amount between 48 and 62 percent by weight when the metal selected is tin and between 36 and 58 percent by weight when the metal selected is antimony, manganese and zirconium in an amount between 4 and 6.5 percent by weight of each when the metal selected is tin and between 3 and 6 percent by weight of each when the metal selected is antimony, the balance being substantially all iron, said alloy being prepared and added to the molten iron bath in such amounts as to produce a final cast product having a silicon content ranging from 1.5 to 2.5 percent by weight and a silicon-to-tin weight ratio between about 46 to 1 and 35 to 1 when the metal selected is tin and a siliconto-antimony weight ratio between about 23 to 1 and 17 to 1 when the metal selected is antimony.

2. A method of treating molten iron for producing iron castings having a type A graphite distribution in a fully pearlitic matrix which comprises adding to a bath of molten iron an alloy consisting essentially of a metal selected from the group consisting of tin and antimony,

the amount of tin in the alloy being between 5 and 20 percent by weight when the metal selected is tin, and the amount of antimony in the alloy being between 10 and 40 percent by weight when the metal selected is antimony, silicon in an amount between 48 and 62 percent by weight when the metal selected is tin and between 36 and 58 percent by weight when the metal selected is antimony, manganese and zirconium in an amount between 4 and 6.5 percent by weight of each when the metal selected is tin and between 3 and 6 percent by weight of each when the metal selected is antimony, up to 5 percent by Weight in the aggregate of modifying metals selected from the group consisting of beryllium, magnesium, calcium, strontium, barium, cerium and aluminum, the balance being substantially all iron, said alloy being prepared and added to the molten iron bath in such amounts as to produce a final cast product having a silicon content of about 2.3 percent by weight and a silicon-to-tin weight ratio of about 46 to 1 when the metal selected is tin and a silicon-to-antimony weight ratio of about 23 to 1 when the metal selected is antimony.

3. A method of treating molten iron for producing iron castings having a type A graphite distribution in a fully pearlitic matrix which comprises adding to a bath of molten iron an alloy consisting essentially by weight of between 14 and 16 percent tin, between 51 and 55 percent by weight silicon, manganese and zironcium in an amount between 4.5 and 6.0 percent by weight of each, the balance being substantially all iron, said alloy being prepared and added to the molten iron bath in such amounts as to produce a final cast product having a silicon content of about 2.3 percent by weight and a silicon-to-tin weight ratio of about 46 to 1.

4. A method of treating molten iron for producing iron castings having a type A graphite distribution in a fully pearlitic matrix which comprises adding to a bath of molten iron an alloy consisting essentially by weight of between 29 and 31 percent antimony, between 42.0 and 45.5 percent by Weight silicon, manganese and zirconium in an amount between 3.5 and 5.0 percent by weight of each, the balance being substantially all iron, said alloy being prepared and added to the molten iron bath in such amounts as to produce a final cast product having a silicon content of about 2.3 percent and a siliconto-antimony weight ratio of about 23 to l.

5. An alloy for treating molten iron for producing iron castings having a type A graphite distribution in a fully pearlitic matrix, said alloy consisting essentially of a metal selected from the group consisting of tin and antimony, the amount of tin in the alloy being between 5 and 20 percent by weight when the metal selected is tin and the amount of antimony in the alloy being between 10 and 40 percent by weight when the metal selected is antimony, silicon in an amount between 48 and 62 percent by weight when the metal selected is tin and between 36 and 58 percent by weight when the metal selected is antimony, manganese and zirconium in an amount between 4.0 and 6.5 percent by weight of each when the metal selected is tin and between 3 and 6 percent by weight of each when the metal selected is antimony, up to 5 percent by weight in the aggregate of modifying metals selected from the group consisting of beryllium, magnesium, calcium, strontium, barium, cerium and aluminum, the balance being substantially all iron.

6. An alloy for treating molten iron for producing iron castings having a type A graphite distribution in a fully pearlitic matrix, said alloy consisting essentially of a metal selected from the group consisting of tin and antimony, the amount of tin in the alloy being between 5 and 20 percent by weight when the metal selected is tin, and the amount of antimony in the alloy being between 10 and 40 percent by weight when the metal selected is antimony, silicon in an amount between 48 and 62 percent by weight when the metal selected is tin and.

between 36and58 percent by weight when the metal selected is antimony, manganese and zirconium in an amount between 4.0 and 6.5 percent by weight of each when the metal selected is tin and between 3 and 6 percent by Weight of each when the metal. selected is antimony, the balance being substantially all iron.

7. An alloy for treating molten iron for producing iron castings having a type A graphite distribution in a fully pearlitic matrix, said alloy consisting essentially by weight of between 14 and 16 percent tin, between :51' and 55 percent by weight silicon, manganese and zirconium in an amount between 4.5 and 6.0 percent by weight of each, the balance being substantially all iron. '8. An alloy for treating molten iron for producing iron castings havinga type A graphite distribution in 'a fully pearlitic matrix, said alloy consisting essentially by weight of between 29 and 31 percent antimony, between 42:0 and 45 percent by weight silicon, manganese and zirconium in anamount between 3.5 and 5.0 percent by weight of each, the balance being substantially all iron.

9. A method of treating molten ironlfo r producing iron-castings having a type A graphite distribution :in a tully pearlitic matrix which comprises adding to a bath of molten ironan alloy consisting essentially of at least 4 Percentage Of tin=m Percentage of tin= lw Lm silicon in an amount between 48 and 62 percent by weight when tin is the only addition metal selected and between 36 and 58 percent by weight when antimony is theonl'y addition metal selected and in amounts proportional to these ranges when tin and'antimony are both selected, manganese and zirconium in an amount between 4.0 and 6.5 percent by weight of each when'tin is the only addition metal selected and between 3 and 6 percent by weight of each when antimony is the only addition metal selected and in amounts proportional to these ranges when tin and antimony are'both selected, the balance being substantially all iron, said alloy being prepared and added to the molten bath in such amounts as to produce a final cast product having a silicon content of about 2.3 percent by weight and a silicon-to-addition metal weight ratio of about '46 to 1 when tin is the only addition metal selected and about 23 to 1 when antimony is the only addition metal selected and in ratios proportional to these when both tin and antimony are selected.

10. A method of treating molten iron for producing iron castings having a type A, graphite distribution in a fully pearlitic matrix which comprises adding to a bath of molten iron an alloy consisting essentially of at least one addition metal selected from the group consisting of tin and antimony, the relative percentage by weight of each metal to be added for a maximum amount of said addition metals being defined by positive solu-' tions' of Equation 1, and the relative percentages by weight of each metal to be added for a minimum amount of said addition metals being defined by positive solu; tions of-Equation2.

(.2) a I 'Percentgge of tin; 10 .percentag2eof'antimony silicon in an amount between 48 and 62 percent by weight when tin is the only addition metal selected and between 36 and 58 percent by weight when antimony is the only addition metal selected and in amounts proportional'to these ranges when tin and antimonyare both selected, manganese and zirconium in an amount between 4.0 and 6.5 percent by weight of each when tin is the only addition metal selected and between 3 and 6 percent y Weight f ach-when an i on i the vonly.additi metal l ed n in mwms i mt ticnal to these n s hen bot t n and ntiin g 'at selec up to 5 P rc n by Weight in the a egat of modi y me a s Selected r m the o p c sis ins 9i ry ium m ium. alcium. s on um. ba um, cerium and al 'm umi e b a ce ein substantial y all ro d a y' be n p e red and dded to the molte i o a in s c amc in s s to produce a fina ast Pr ct having a s l con conten ran in tram bou 1.5 to 2.5 percent'by weight and a siIicon-to-addition metal weight ratio between 46 to 1 and 35 to '1 when tin is the only addition metal selected, and between 23 to 1 and -l7 to 1 When antimony is the only addition metal selected, and in ratios proportional to these ratios when both tin and antimony are selected.

11. A method of treating molten iron for producing iron castings having a type A graphite distribution in a fully pearlitic matrix which comprises adding to a bath of molten iron an alloy consisting essentially'of at least one addition metal selected from the group consisting o na nt m y t l ti Percen age b Wei of each metal to be added for a maximum amount of said addition metals being defined by positive solutions of Equation 1, and the relative percentages by weight of each metal to be added for a'minimum amount of said addition metals being defined by positive solutions of Equation 2,

Percentage of tin=4w Percentage of tin: Hw

silicon in an amount such that Z (2X 4- Y) i=6 wherein Z represents the increase in silicon content after addition of the alloy, X the percent by weight of tin and Y the percent by weight of antimony, manganese and zirconium in an amount between 4.0 and 6.5 percent by weight of each when tin is the only addition metal selected and between f3 and 6 percent by weight of each when antimony is the only addition metal selected and in amounts proportional to these ranegs when tin and antimony are both selected, the balance being substantially all iron. v

12, An alloy for treating molten iron-for producing iron castings having a type A graphite distribution in a fully pearlitic matrix, said alloy consisting essentially of at least one addition metal selected from the group consisting of tin and antimony, the relative percentages by weight of each metal to be added for maximum amount of said addition metals being defined bypositive solutions of Equation 1, and the relative percentages by g t of each metal to be added when a minimum a e-q.

Percentage of tin: 10-percentage of antimony silicon in an amount between 48 and 62 percent by weight when tin is the only addition metal selected and between 36 and 58 percent by weight when antimony is the only addition metal selected and in amounts proportional to these ranges when tin and antimony are both selected, manganese and zirconium in an amount between 4.0 and 6.5 percent by weight of each when tin is the only additional metal selected and between 3 and 6 percent by Weight of each when antimony is the only addition metal selected and in amounts proportional to these ranges when tin and antimony are both selected, the balance being substantially all iron.

13. An alloy for treating molten iron for producing iron castings having a type A graphite distribution in a fully pearlitic matrix, said alloy consisting essentially of at least one addition metal selected from the group con sisting of tin and antimony, the relative percentages by Weight of each metal to be added for a maximum amount of said addition metals being defined by positive solutions of Equation 1, and the relative percentages by Weight of each metal to be added for a minimum amount of said addition metals being defined by positive solutions of Equation 2,

Percentage of 40percentage of antimony silicon in an amount between 48 and 62 percent by weight when tin is the only addition metal selected and between 36 and 58 percent by weight when antimony is the only addition metal selected and in amount proportional to these ranges when tin and antimony are both selected, manganese and zirconium in an amount between 4.0 and 6.5 percent by weight of each when tin is the only addition metal selected and between 3 and 6 percent by weight of each when antimony is the only addition metal selected and in amount proportional to these ranges when both tin and antimony are selected, up to percent by Weight in the aggregate of modifying metals selected from the group consisting of beryllium, magnesium, calcium, strontium, barium, cerium, and aluminum, the balance being substantially all iron.

14. An alloy for treating molten iron for producing iron castings having a type A graphite distribution in a fully pearlitic matrix, said alloy consisting essentially of at least one addition metal selected from the group consisting of tin and antimony, the relative percentages by weight of each metal to be added for a maximum amount of said addition metals being defined by positive solutions of Equation (1), and the relative percentages by Weight of each metal to be added when a minimum amount of said addition metals being defined by positive solutions of Equation 2,

Percentage of 40percentage of antimony Percentage of tin: 10-peroentage of antimony wherein Z represents the increase in silicon content after addition of the alloy, X the percent by weight of tin and Y the percent by weight of antimony, manganese and zirconium in an amount between 4.0 and 6.5 percent by weight of each when tin is the only addition metal selected and between 3 and 6 percent by weight of each when antimony is the only addition metal selected and in amounts proportional to these ranges when tin and antimony are both selected, the balance being substantially all iron.

15. An alloy for treating molten iron for producing iron castings having a type A graphite distribution in a full pearlitic matrix, said alloy consisting essentially of at least one addition metal selected from the group consisting of tin and antimony, the relative percentages by weight of each metal to be added when a maximum amount of said addition metals being defined by positive solutions of Equation 1, and the relative percentages by Weight of each metal to be added With a minimum amount of said addition metals being defined by positive solutions of Equation 2,

40- ercenta e of antimon Percentage of trn= l isilicon in an amount between 48 and 58 percent by weight, manganese and zirconium in an amount between 4 and 6 percent by weight of each, the balance being substantially all iron.

References Cited inthe file of this patent UNITED STATES PATENTS 2,515,822 Crome July 18, 1950 

6. AN ALLOY FOR TREATING MOLTEN IRON FOR PRODUCING IRON CASTINGS HAVING A TYPE A GRAPHITE DISTRIBUTION IN A FULLY PEARLITIC MATRIX, SAID ALLOY CONSISTING ESSENTIALLY OF A METAL SELECTED FROM THE GROUP CONSISTING OF TIN AND ANTIMONY, THE AMOUNT OF TIN IN THE ALLOY BEING BETWEEN 5 AND 20 PERCENT BY WEIGHT WHEN THE METAL SELECTED IS TIN, AND THE AMOUNT OF ANTIMONY IN THE ALLOY BEING BETWEEN 10 AND 40 PERCENT BY WEIGHT WHEN THE METAL SELECTED IS ANTIMONY, SILICON IN AN AMOUNT BETWEEN 48 AND 62 PERCENT BY WEIGHT WHEN THE METAL SELECTED IS TIN AND BETWEEN 36 AND 58 PERCENT BY WEIGHT WHEN THE METAL SELECTED IS ANTIMONY, MANGANESE AND ZIRCONIUM IN AN AMOUNT BETWEEN 4.0 AND 6.5 PERCENT BY WEIGHT OF EACH WHEN THE METAL SELECTED IS TIN AND BETWEEN 3 AND 6 PERCENT BY WEIGHT OF EACH WHEN THE METAL SELECTED IS ANTIMONY, THE BALANCE BEING SUBSTANTIALLY ALL IRON. 